There is a imperative necessity of and strong demand for a liquid level sensor, that continuously measures the level of a liquid contained in a tank or reservoir in an accurate and reliable manner, whereby it provides a means for inventorying the liquid medium stored in the tank or reservoir in collaboration with flowmeters measuring in and out flows of the liquid medium therein. For example, an accurate and reliable liquid level sensor can be used as a leak detector for the underground gasoline or diesel fuel tanks, as the discrepancy between the flow data deducted from the liquid level sensor and the flow data provided by the custody transfer flowmeters provides an indication whether the gasoline or diesel fuel is being lost by a leak or evaporation.